Two-stage combustor for thermophotovoltaic generator

ABSTRACT

A thermophotovoltaic generator incorporating a two-stage combustor for providing heat to a thermophotovoltaic cell. Combustor parts include a partial oxidation reactor, which functions catalytically to convert a hydrocarbon fuel and a first supply of an oxidant into a gaseous partial oxidation product; and further include downstream thereof, a deep oxidation reactor including a premixer plenum fluidly connected to a heat spreader comprising a porous matrix, such as a ceramic foam. Functionally, the deep oxidation reactor converts the gaseous partial oxidation product and a second supply of oxidant into complete combustion products. Heat produced by the two-stage combustor generates radiative energy from a photon emitter, which is directly converted to electricity in a photovoltaic diode cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/798,630, filed Feb. 24, 2020, which claims the benefit of U.S.Provisional Application No. 62/813,801, filed Mar. 5, 2019. Theaforementioned applications in their entirety are incorporated herein byreference.

GOVERNMENT RIGHTS

This invention was made with support from the U.S. government underContract No. W911QX-17-P-0163, sponsored by the Department of Defense.The U.S. Government holds certain rights in this invention.

FIELD OF THE INVENTION

This invention pertains to a thermophotovoltaic (TPV) generator thatfunctions to produce heat, light and electricity. This invention alsopertains to a combustor that generates the heat in thethermophotovoltaic generator. Thermophotovoltaic generators are usefulfor electricity-generating applications in off-grid locations, that is,where an electrical grid is unavailable or temporarily disrupted, asmight be found in logistics operations involving military and rescuemaneuvers. Thermophotovoltaic generators are also useful when a quietpower source with a low acoustic signature is desired, as for example incovert operations and submarine auxiliary power applications. Since TPVgenerators lack heavy moving parts and provide advantageous power perunit weight, TPV generators are also useful in applications where weightand portability are considerations, as might be found in spacecraft andspace probes. Finally, uses can also be found to incorporate TPVgenerators into common-place applications as electricity-cogeneratingunits alongside, for example, gas turbines, residential burners andappliances, and in hybrid vehicles.

BACKGROUND OF THE INVENTION

Thermophotovoltaic (TPV) generators convert thermal energy directly intoelectricity without any intermediate working substance and withoutmoving parts. Typically, a combustor burning a hydrocarbon fuel providesthe thermal energy needed to actuate a TPV cell comprised of (a) anemitter that spontaneously emits photon radiation in response to thermalexcitation of charges in the emitter material, and (b) at least onephotovoltaic diode that absorbs the photons thereby initiating aphotoelectric reaction and generating a flow of electricity. The thermalemitter exhibits a peak electromagnetic wavelength and a total radiatedenergy density depending upon the temperature of the emitter accordingto Wien's law. As temperature increases, peak wavelength shifts fromlonger wavelengths to shorter wavelengths; while energy densityincreases exponentially. Thermal emitters operate reliably at atemperature between about 900° C. and 1,400° C. Typically, the TPVgenerator comprises a plurality of TPV cells disposed in close proximityacross a heated surface of the combustor.

Stable, non-catalytic combustion of a hydrocarbon fuel, like naturalgas, at ambient pressure in a single stage combustor requires anear-stoichiometric ratio of the oxidant relative to the hydrocarbonfuel. The term “stoichiometric ratio” refers herein to an exact ratio ofmoles of oxidant to moles of hydrocarbon fuel required to convert all ofthe fuel to complete (or deep) oxidation products, namely, carbondioxide and water. For methane, the stoichiometric ratio equals 2 molesmolecular oxygen (O₂) per mole methane (CH₄). “Near-stoichiometric”molar ratios for methane combustion could range from about 1.6 molesmolecular oxygen per mole methane (1.6:1) to about 2.4:1, which ratioscorrelate to a phi (φ) of 0.8:1 to about 1.2:1, where phi compares theactual molar ratio employed to the stoichiometric ratio. Such highratios of oxidant to fuel result in a flame temperature exceeding 1,200°C., which is typically too hot for metallic materials of construction.As a further disadvantage, single stage combustors operating onconventional hydrocarbon fuels can exhibit fluctuations in temperatureand non-uniformity in temperature distribution within the combustor.These attributes are particularly disadvantageous when the combustor isassociated with an array of photon emitters in a TPV generator, becausesteady and uniform photon emission requires a steady and uniformtemperature across the combustor.

Additionally, while combustion in the presence of a catalyst in a singlestage combustor is useful in promoting complete conversion and improvedselectivity of the combustion process, catalyst lifetime is greatlyreduced in an oxidizing environment at temperatures exceeding 1,200° C.Generally, catalyst lifetime is lengthened as temperature decreases.Moreover, at temperatures exceeding 1,200° C. the catalyst may be lostthrough volatilization.

In view of the above, it would be desirable to design an improvedcombustor apparatus for use in a thermophotovoltaic generator. Thecombustor should provide for complete combustion of a hydrocarbon fuelinto a mixture of carbon dioxide and water with minimal, if any,emissions of NOx and hydrocarbons. The design should take into accountmaterials of construction suitable for operation at ambient pressure anda temperature of at least 1,000° C., and more preferably, up to about1,200° C. If such a combustor were to employ an oxidation catalyst forimproved conversion and selectivity, then under operating conditions thecatalyst should sustain an acceptable durability and lifetime atoperating temperatures, before needing to be replaced. Finally, in orderto provide improvements for TPV applications, the design shouldincorporate structural features for efficiently transferring the thermalheat produced in the combustor to the photon emitter. Such featuresshould provide for reduced fluctuations in temperature within thecombustor as well as a more uniform temperature distribution across thecombustor so as to ensure a steady and uniform emission of photons fromthe photon emitter.

SUMMARY OF THE INVENTION

In one aspect, this invention provides for a two-stage combustorcomprising:

(a) a partial oxidation reactor, comprising the following components:

-   -   (i) a fuel inlet,    -   (ii) a first oxidant inlet,    -   (iii) a partial oxidation reaction zone comprising a mesh        substrate having a partial oxidation catalyst supported thereon,        the partial oxidation reaction zone being disposed in fluid        communication with the fuel inlet and first oxidant inlet, and    -   (iv) an outlet fluidly connected to the partial oxidation        reaction zone; and

(b) a deep oxidation reactor comprising the following components:

-   -   (i) a premixer plenum having an upstream end and a downstream        end; wherein at the upstream end the premixer plenum is fluidly        connected to the outlet of the partial oxidation reactor; and        further wherein the premixer plenum comprises a second oxidant        inlet;    -   (ii) a heat spreader having an upstream end and a downstream        end; wherein at the upstream end the heat spreader is fluidly        connected to the downstream end of the premixer plenum; and        further wherein the heat spreader comprises a porous matrix        capable of withstanding a temperature greater than about 900°        C.; and    -   (iii) an outlet pathway fluidly connected to the downstream end        of the heat spreader.

In another aspect, this invention provides for a thermophotovoltaicgenerator comprising: (1) a two-stage combustor; (2) a photon emitterdisposed in thermal communication with the two-stage combustor; and (3)at least one photovoltaic diode cell disposed in radiative communicationwith the photon emitter;

wherein the two-stage combustor comprises:

(a) a partial oxidation reactor comprising the following components:

-   -   (i) a fuel inlet,    -   (ii) a first oxidant inlet,    -   (iii) a partial oxidation reaction zone comprising a mesh        substrate having a partial oxidation catalyst supported thereon,        the partial oxidation reaction zone being disposed in fluid        communication with the fuel inlet and the first oxidant inlet,        and    -   (iv) an outlet fluidly connected to the partial oxidation        reaction zone; and

(b) a deep oxidation reactor comprising the following components:

-   -   (i) a premixer plenum having an upstream end and a downstream        end; wherein at the upstream end the premixer plenum is fluidly        connected to the outlet of the partial oxidation reactor; and        further wherein the premixer plenum comprises a second oxidant        inlet;    -   (ii) a heat spreader having an upstream end and a downstream        end; wherein at the upstream end the heat spreader is fluidly        connected to the downstream end of the premixer plenum; and        further wherein the heat spreader comprises a porous matrix        capable of withstanding a temperature greater than about 900°        C.; and    -   (iii) an outlet pathway fluidly connected to the downstream end        of the heat spreader.

The two-stage combustor of this invention functionally splits thecombustion of a hydrocarbon fuel into two process segments. A firststage of the combustor comprises a partial oxidation reactor whereinunder operating conditions partial oxidation (POX) occurs, such that ahydrocarbon fuel is oxidized into a gaseous partial oxidation productcomprising predominantly carbon monoxide and hydrogen. A second stage ofthe combustor comprises a deep oxidation reactor wherein under operatingconditions complete combustion occurs, either catalytically ornon-catalytically, so as to convert the gaseous partial oxidationproduct into complete oxidation products of carbon dioxide and waterwith advantageously low levels of undesirable NOx and hydrocarbonsemissions. Additionally, the two-stage combustor functions in the TPVgenerator to deliver thermal energy (heat) to the photon emitter of athermophotovoltaic cell resulting in generation of electricity.

In one advantageous embodiment, a catalyst is disposed only within thepartial oxidation reactor; whereas the deep oxidation reactor does notcontain a catalyst. Suitable partial oxidation catalysts including thoseof the noble metal family are able to withstand temperatures ofcatalytic partial oxidation processes, which are generally less than1,100° C. and, more likely, between 850° C. and about 1,050° C. Theselower temperatures and reducing conditions advantageously provide forcatalyst durability and longevity as well as high selectivity tohydrogen and carbon monoxide products. As well, at these lowertemperatures and under the reducing and fuel-rich conditions of POXreactions, the catalyst is less prone to decay and losses throughvolatilization. Further in this embodiment, the second stage deepoxidation reactor is operated non-catalytically allowing for sustainedhigher temperatures of greater than about 900° C., and in certainembodiments greater than about 1,000° C. up to 1,400° C., as dictated bythe deep oxidation process. This then results in more completecombustion while avoiding catalyst degradation problems.

In an alternative embodiment, both the POX and the deep oxidationreactors utilize a catalyst. In this instance, the catalyst located inthe deep oxidation reaction is selected from sturdier catalyticmaterials, which better tolerate the higher temperatures and oxidationreaction conditions.

As another advantage, hydrogen generated in the first stage POX reactorprovides for improved combustion stability in the second stage deepoxidation reactor. This in turn provides advantageously for reducedfluctuations in temperature within the combustor as well as a moreuniform temperature distribution across the combustor, whichbeneficially results in a steadier and more uniform emission of photonsacross the photon emitter. Finally, specific structural features of thecombustor result in efficient heat transfer to the photon emitter,thereby providing for efficient radiative emission of photons andconversion of photonic energy directly into electricity in thephotovoltaic diode(s).

DRAWINGS

FIG. 1 depicts in isometric view an exemplary embodiment of thetwo-stage combustor apparatus of this invention in association with aTPV emitter.

FIG. 2 depicts the exemplary embodiment of FIG. 1 in a transversecross-sectional view.

FIG. 3 illustrates in isometric view another exemplary embodiment of thethermophotovoltaic generator of this invention including a heatrecuperation structure.

FIG. 4 illustrates in isometric view another exemplary embodiment of thethermophotovoltaic generator of this invention.

FIG. 5 depicts a graph plotting temperature as a function of time duringoperation of an embodiment of the two-stage combustor-emitter section ofthe TPV generator of this invention.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment, this invention provides for a thermophotovoltaicgenerator comprising: (1) a two-stage combustor; (2) a photon emitterdisposed in thermal communication with the two-stage combustor; and (3)at least one photovoltaic diode cell disposed in radiative communicationwith the photon emitter;

wherein the two-stage combustor comprises:

-   -   (a) a partial oxidation reactor comprising:        -   (i) a fuel inlet for feeding a hydrocarbon fuel into a            partial oxidation reaction zone,        -   (ii) a first oxidant inlet for feeding a first supply of an            oxidant into the partial oxidation reaction zone,        -   (iii) the partial oxidation reaction zone comprising a mesh            substrate having a partial oxidation catalyst supported            thereon, the partial oxidation reaction zone being in fluid            communication with the fuel inlet and the first oxidant            inlet; and        -   (iv) an outlet fluidly connected to the partial oxidation            reaction zone for exhausting a partial oxidation product;            and    -   (b) a deep oxidation reactor comprising:        -   (i) a premixer plenum having an upstream end and a            downstream end; wherein at the upstream end the premixer            plenum is fluidly connected to the outlet of the partial            oxidation reactor; and further wherein the premixer plenum            comprises a second oxidant inlet for feeding a second supply            of an oxidant into the premixer plenum;        -   (ii) a heat spreader having an upstream end and a downstream            end; wherein at the upstream end the heat spreader is            fluidly connected to the downstream end of the premixer            plenum; and further wherein the heat spreader comprises a            ceramic foam matrix capable of withstanding a temperature            greater than about 1,000° C., which is disposed in thermal            communication with the photon emitter; and        -   (iii) an outlet pathway fluidly connected to the downstream            end of the heat spreader for exhausting a gaseous combustion            product.

The term “upstream end” signifies a side or inlet of a specifiedcomponent in the two-stage combustor wherein a fluid flow enters thecomponent. The term “downstream end” signifies a side or outlet of aspecified component in the two-stage combustor wherein a fluid flowexits the component.

It should be appreciated that under operating conditions thermal energygenerated in the two-stage combustor is transferred to the photonemitter, which upon thermal excitation emits photons generally in aninfrared region of the electromagnetic spectrum. To facilitate thermaltransfer from the combustor to the photon emitter, the heat spreader ofthe deep oxidation combustor is disposed in thermal communication withthe photon emitter, typically in close proximity to the photon emitter.The phrase “in close proximity” means that the heat spreader, in oneexemplary embodiment, physically contacts the photon emitter. In anotherembodiment, the phrase “in close proximity” means that the heat spreaderdoes not physically contact the photon emitter, but rather a small gapexists between the two components. In this embodiment, the gap is sizedsuch that gaseous streams flow freely through the gap, while allowingfor thermal heat transfer from the heat spreader to the photon emitterto remain acceptably efficient.

Photon emission depends upon chemical composition of the emitter andupon temperature. For a selected chemical composition and selectedtemperature, a curve can be generated or found in the art definingintensity of photonic emission as a function of wavelength. Generally,the curve peaks at a particular wavelength. A set of such curves can begenerated for a given composition and a set of selected temperatures. Tofacilitate efficient photon emission in this invention, the operatingtemperature of the deep oxidation reactor is tuned to an appropriatepeak emission temperature of the selected emitter. Conversely, one canselect an emitter that exhibits a peak emission at the intendedoperating temperature of the deep oxidation reactor.

In one preferred embodiment of this invention, the deep oxidationreactor does not comprise a catalyst. In such instance, the combustionprocess within the deep oxidation reactor is non-catalytic. By avoidingthe use of a catalyst in the deep oxidation reactor (both in thepremixer plenum and in the heat spreader) where temperatures are attheir highest, the apparatus avoids problems associated with catalystvolatilization and degradation.

Functionally, it is desirable to have the combustion occur in the heatspreader, which is positioned in thermal communication with the photonemitter, for example, in close proximity to the photon emitter. Undersome operating conditions, however, diffusion flame combustion mightoccur within the premixer plenum. To avoid a diffusion flame combustionwithin the premixer plenum, a flame arrestor can be positioned withinthe premixer plenum. In any case, the premixer plenum does not contain afoam matrix or a catalyst.

Features of this invention are further defined and clarified byconsideration of the following figures and embodiments. Reference ismade to FIG. 1 illustrating in isometric view an exemplary embodiment100 of the TPV generator of this invention comprising the two-stagecombustor apparatus of this invention in association with a TPV emitter.See also FIG. 2 illustrating the same embodiment in transversecross-sectional view. The TPV generator 100 comprises a partialoxidation reactor 1 fitted with a fuel inlet 2 for feeding a hydrocarbonfuel into a partial oxidation reaction zone 11 and fitted with a firstoxidant inlet 3 for feeding a supply of a first oxidant into the partialoxidation reaction zone 11. The partial oxidation reaction zone 11comprises a mesh substrate 12 having a reforming catalyst 14 supportedthereon. Glow plug 4 is positioned at the upstream inlet end of thepartial oxidation reaction zone 11 for initiating a catalytic partialoxidation reaction therein. The downstream end of the partial oxidationreactor 1 provides an outlet 5 for exhausting partial oxidation reactionproducts (reformed fuel products) comprising predominantly hydrogen (H₂)and carbon monoxide (CO).

With further reference to FIGS. 1 and 2 , the deep oxidation reactorcomprises a premixer plenum 7, which at its upstream end is fluidlyconnected to the outlet 5 of the partial oxidation reactor 1. Thepremixer plenum 7 is further comprised of a second oxidant inlet 6 forfeeding a second supply of oxidant into the premixer plenum 7. The heatspreader 8 is disposed in fluid communication with the downstream end ofthe premixer plenum 7 and comprises a porous matrix capable ofwithstanding a temperature greater than 900° C., in this instance shapedas a circular layer. Downstream from the heat spreader 8 is outlet gappathway 16, from which deep combustion gases (CO₂ and H₂) are exhaustedwith minimal NOx and hydrocarbons emissions. Proximate to the heatspreader 8 is disposed an array of TPV cells 9, comprising an emitterthat functions to emit photons and least one, and preferably, aplurality of diode photovoltaic cells that collect the emitted photonsand convert them into electricity.

Reference is made to FIG. 3 illustrating in isometric view anotherexemplary embodiment 200 of the thermophotovoltaic generator of thisinvention comprising a two-stage combustor associated with an array ofTPV cells. Apparatus 200 comprises a partial oxidation reactor 10 fittedwith a fuel inlet 20 and a first oxidant inlet 30 for feeding suppliesof fuel and the first oxidant, respectively, into the POX reactor 10.The downstream end of the partial oxidation reactor 10 provides anoutlet 50 for exhausting the partial oxidation reaction products(reformed fuel products). FIG. 3 does not illustrate the interior of thePOX reactor 10, which comprises, in similar fashion to FIG. 2 , apartial oxidation reaction zone 11 comprising a mesh substrate 12 havinga POX catalyst 14 supported thereon.

Further to FIG. 3 , the deep oxidation reactor comprises a premixerplenum 70, which at its upstream end is fluidly connected to the outlet50 of the partial oxidation reactor 10. The premixer plenum 70 isfluidly connected to the second oxidant inlet 60 for feeding a secondsupply of oxidant into the premixer plenum 70. The heat spreader 80 isdisposed in fluid communication with the downstream end of the premixerplenum 70. In fluid communication with the heat spreader 80 is outletpathway 160, from which combustion gases are exhausted. Proximate to theheat spreader 80 is disposed an array of TPV cells 90, functioning toemit photons via an emitter and convert said photons to electricity viaan array of diode photovoltaic cells. FIG. 3 further illustrates a heatrecuperation structure, wherein the combustion exhaust outlet 160extends through an exhaust passage bounded by a thermally conductivewall 110 to final exhaust outlet 180. The thermally conductive wall iscapable of transmitting heat from the hot exhausting combustion productsto the cool incoming second supply of oxidant entering through inlet 60and flowing on the opposite side of thermally conductive wall 110towards the premixer plenum 70. Insulation 120 surrounds the entiretwo-stage combustor so as to retard heat losses to the environment.Refer to FIG. 5 of U.S. Pat. No. 8,749,508, incorporated herein byreference, illustrating in higher detail construction of the thermallyconductive wall 110, which is typically provided in a verticalcorrugated structure.

Reference is made to FIG. 4 illustrating yet another embodiment 300 ofthe thermophotovoltaic generator of this invention, which is constructedconcentrically to provide for radial fluid flow. Apparatus 300 comprisesa partial oxidation reactor 310 fitted with a fuel inlet 320 and a firstoxidant inlet 330 for feeding supplies of fuel and first oxidant,respectively, into the POX reactor 310. The downstream end of thepartial oxidation reactor 310 provides an outlet 350 for exhausting thepartial oxidation reaction products into a porous chamber 355 allowingfor a radial flow passage. FIG. 4 does not illustrate the interior ofthe POX reactor 310, which comprises in similar fashion to FIG. 2 , apartial oxidation reaction zone 11 comprising a mesh substrate 12 havinga POX catalyst 14 supported thereon. Further to FIG. 4 , the deepoxidation reactor comprises a premixer plenum 370, which at its upstreamside is fluidly connected to the porous chamber 355, such that reactionproducts flow radially outward from the porous chamber 355 into thepremixer plenum 370. Second oxidant inlet 360 feeds a second supply ofoxidant into the premixer plenum 370. A porous heat spreader 380 isdisposed in fluid communication via radial flow with the downstream sideof the premixer plenum 370. Proximate to the heat spreader 380 isdisposed an array of TPV cells 390. Combustion gases exhaust the porousheat spreader 380 via exit through a recuperator 385.

Each component of the two-stage combustor apparatus of this invention isconstructed from a material capable of withstanding the temperatures towhich the relevant part is to be exposed. Moreover, each part isdesigned to maximize heat transfer downstream to the heat spreader, fromwhich thermal energy is efficiently transferred to a photon emitter.Typically, the first stage partial oxidation reactor and second stagedeep oxidation reactor are combined within a housing that is constructedfrom a material capable of withstanding temperatures up to 1,400° C.,preferably up to 1,200° C., for prolonged periods. Such metals includeiron-chromium alloys (FeCrAlY); nickel-chromium alloys andnickel-chromium-iron alloys, such alloys to include HASTELLOY® brandalloys (Haynes International) including HASTELLOY brand Alloy X(“HastX”), INCONEL® brand alloys (Huntington Alloys, Inc.) includingINCONEL brand Alloy 625, INCONEL brand Alloy 718, INCONEL brand Alloy600, and INCONEL brand Alloy 601, as well as stainless steel whentemperature permits. The fuel and oxidant inlets to the partialoxidation reactor and the secondary oxidant inlet to the premixer plenumare constructed, likewise, from any of the above-identified alloys, butcan also be satisfactorily constructed from standard stainless steel orhigh temperature stainless steel in those instances where the inlets areexposed to temperatures not exceeding about 800° C. The housing of thetwo-stage combustor is typically lined with an insulator at least on itsinterior surface, if not also its exterior surface, so as to minimizelosses of combustion heat to the surrounding environment. Suitableinsulators include high temperature ceramic fiber insulation,non-limiting examples of which include KAOWOOL® brand ceramic fiberinsulation (Thermal Ceramics, Inc.) and high temperature aerogelinsulation, such as PYROGEL® brand aerogel insulation (Aspen Aerogels,Inc.). The combustor external exhaust outlet (FIG. 3 /180), which isexposed to temperatures of about 150° C. to 250° C., typically employs ametallic construction material of suitable thermal durability, includingany of the aforementioned alloys. In the embodiment of FIG. 3 , whereinthe secondary oxidant inlet 60 pathway to the premixer plenum 70 sharesa common thermally-conductive wall 110 with the combustor exhaustpathway (connecting internal outlet 160 to external outlet 180), thewall is typically comprised of a HASTELLOY brand Alloy X, or a FeCrAlYiron-chromium alloy, or stainless steel, any one of which is suitablyprovided as a thin wall or foil sheet.

The partial oxidation reactor beneficially employed in the process ofthis invention comprises any one of those partial oxidation (POX)reactors known in the art that is capable of converting the mixture ofhydrocarbon fuel and the first oxidant into a gaseous partial oxidationproduct comprising hydrogen and carbon monoxide. Non-limiting examplesof suitable partial oxidation reactors include those described in thefollowing patent documents: U.S. Pat. Nos. 7,976,594; 8,557,189; WO2004/060546; and US 2011/0061299, incorporated herein by reference.

According to the invention, under operating conditions the hydrocarbonfuel is fed from a fuel supply, such as a fuel tank, through a firstinlet into the partial oxidation reactor, preferably, into a mixerwithin the partial oxidation reactor. The fuel inlet comprises any knowninlet device for feeding the hydrocarbon fuel, for example, a nozzle,atomizer, vaporizer, injector, mass flow meter, or any other suitableflow control device. The injector also functions to quantify (or meter)the fuel fed to the partial oxidation reactor. Likewise, the firstsupply of oxidant is fed into the partial oxidation reactor, preferably,into the mixer section of the partial oxidation reactor, through thefirst oxidant inlet comprising any conventional inlet device, forexample, a nozzle, injector, or mass flow meter capable of feeding theoxidant into the partial oxidation reactor.

In one embodiment, the mixer of the partial oxidation reactor comprisesswirler vanes and baffles to facilitate mixing the hydrocarbon fuel andoxidant as well as to facilitate atomization of any liquid fuel, when aliquid fuel is employed. In one other embodiment, the mixer comprises acombination of a pulsed electromagnetic liquid fuel injector and apulsed oxidant injector, which feed the liquid fuel and first supply ofoxidant, respectively, into an atomizer that thoroughly atomizes theliquid fuel and mixes it with the oxidant. This combined dualinjector-atomizer device is described in U.S. Pat. No. 8,439,990,incorporated herein by reference. If a gaseous hydrocarbon fuel isemployed, there is no requirement to provide an atomizer.

In one embodiment, the hydrocarbon fuel is fed to the mixer at ambienttemperature without preheating. In another embodiment, the hydrocarbonfuel is preheated prior to being fed to the mixer. In the event that aliquid hydrocarbon fuel is employed, we have found that heat generatedin the reaction zone of the partial oxidation reactor is sufficient tosupport liquid fuel vaporization at a level required for stable partialoxidation throughout the partial oxidation catalyst. As a consequence,the partial oxidation reactor and POX process therein providegasification of a liquid fuel without a requirement for supplyingexternal heat or steam to the partial oxidation reactor. The firstsupply of oxidant is generally fed into the mixer without preheating,but variations in temperature may be implemented as desired.

The partial oxidation reactor comprises a catalytic reaction zone havingdisposed therein a porous substrate onto which a partial oxidationcatalyst is supported, such porous substrate configured to providethorough mixing of the fuel and oxidant passing there through. Toachieve this goal, in one embodiment the substrate is provided as a meshsubstrate, structured as a reticulated net or reticulated screencomprising a plurality of pores or cells or channels, preferably, havingan ultra-short-channel-length as noted hereinafter. In one embodiment,the mesh is suitably provided in a coiled configuration of cylindricalshape having an inner diameter and a larger outer diameter such thatreactants flowing there through move along a radial flow path from aninlet along the inner diameter to an outlet along the outer diameter ofthe coil. In another embodiment the mesh is suitably provided as onemesh sheet or a plurality of stacked mesh sheets with a bulk flow froman inlet end of the stack to an outlet end of the stack. In anyembodiment, the bulk configuration of the substrate provides for aplurality of void volumes in random order, that is, empty spaces havingessentially no regularity along the flow path from the partial oxidationreactor upstream inlets to the partial oxidation reactor downstreamoutlet.

In one exemplary embodiment, the substrate comprises anultra-short-channel-length mesh; in a more preferred embodiment thereofa MICROLITH® brand ultra-short-channel-length mesh (PrecisionCombustion, Inc., North Haven, Conn., USA). A description of theultra-short-channel-length mesh is found, for example, in U.S. Pat. No.5,051,241, incorporated herein by reference. Generally, the meshcomprises short channel length, low thermal mass monoliths, whichcontrast with prior art monoliths having longer channel lengths. Forpurposes of this invention, the term “ultra-short-channel-length” refersto a channel length in a range from about 25 microns (μm) (0.001 inch)to about 500 μm (0.02 inch). In contrast, the term “long channels”pertaining to prior art monoliths refers to channel lengths of greaterthan about 5 mm (0.20 inch) upwards of 127 mm (5 inches). In thisinvention the term “channel length” is taken as the distance along apore or channel from inlet to outlet, for example, as measured from aninlet on one side of a sheet of mesh to an outlet on another side of thesheet. (This measurement is not to be confused with the overall lengthof the flow path through the entire mesh substrate from the upstreaminlet of the substrate to the downstream outlet of the substrate.) Inanother embodiment, the channel length of the mesh is no longer than thediameter of the elements from which the mesh is constructed; thus, thechannel length may range from 25 μm (0.001 inch) up to about 100 μm(0.004 inch) and preferably not more than about 350 μm (0.014 inch). Inview of this ultra-short channel length, the contact time of reactantswith the mesh and catalyst supported thereon advantageously ranges fromabout 5 milliseconds (5 msec) to about 350 msec.

The MICROLITH brand ultra-short-channel-length mesh typically comprisesfrom about 100 to about 1,000 or more flow channels per squarecentimeter. More specifically, each layer of mesh typically isconfigured with a plurality of channels or pores having a diameterranging from about 0.25 millimeters (mm) to about 1.0 mm, with a voidspace greater than about 60 percent, preferably up to about 80 percentor more. A ratio of channel length to diameter is generally less thanabout 2:1, preferably less than about 1:1, and more preferably, lessthan about 0.5:1. MICROLITH brand meshes can be manufactured in the formof woven wire screens, woven ceramic fiber screens, pressed metal orceramic screens; or they can be manufactured by perforation andexpansion of a thin metal sheet as disclosed in U.S. Pat. No. 6,156,444,incorporated herein by reference; or alternatively manufactured by 3-Dprinting or by a lost polymer skeleton method.

The MICROLITH brand mesh having the ultra-short-channel-lengthfacilitates packing more active surface area into a smaller volume andprovides increased reactive area and lower pressure drop, as comparedwith prior art monolithic substrates. Whereas in prior art honeycombmonoliths having conventional long channels where a fully developedboundary layer is present over a considerable length of the channels; incontrast, the ultra-short-channel-length characteristic of the mesh ofthis invention avoids boundary layer buildup. Since heat and masstransfer coefficients depend on boundary layer thickness, avoidingboundary layer buildup enhances transport properties. Employing theultra-short-channel-length mesh, such as the MICROLITH brand thereof, tocontrol and limit the development of a boundary layer of a fluid passingthere through is described in U.S. Pat. No. 7,504,047, which is aContinuation-In-Part of U.S. Pat. No. 6,746,657 to Castaldi, bothpatents incorporated herein by reference. The preferred MICROLITH brandof ultra-short-channel-length mesh also advantageously provides for alight-weight portable size, a high throughput, a high one-pass yield ofhydrogen-containing partial oxidation product, a low yield of coke andcoke precursors, and an acceptably long catalyst lifetime, as comparedwith alternative substrates including ceramic monolith and pelletedsubstrates.

The mesh is typically constructed from any material capable ofwithstanding the temperature at which the reforming zone operates,generally, in a range from about 750° C. to about 1,200° C. Suchmaterials include metals and ceramic materials of suitable temperaturedurability. Suitable metal meshes include, without limitation, thoseconstructed from nickel-chromium-iron alloys, iron-chromium alloys, andiron-chromium-aluminum alloys. The term “ceramic” refers to inorganicnon-metallic solid materials with prevalent covalent bonds, includingbut not limited to metallic oxides, such as oxides of aluminum, silicon,magnesium, zirconium, titanium, niobium, and chromium, as well aszeolites and titanates. Reference is made to U.S. Pat. Nos. 6,328,936and 7,141,092, detailing insulating layers of ultra-short-channel-lengthceramic mesh comprising woven silica, both patents incorporated hereinby reference.

In another exemplary embodiment, the porous substrate is constructed ofan analogous porous structure of metal, ceramic, or other porousstructured substrate material having an ultra-short-channel length,comprising an interconnected network of solid struts defining aplurality of pores of an open-cell configuration. The pores can have anyshape or diameter; but typically, a number of pores that subtend oneinch designates a “pore size,” which for most purposes ranges from about5 to about 80 pores per inch. The relative density of such structures,taken as the density of the porous structure divided by the density ofsolid parent material of the struts, typically ranges from about 2 toabout 15 percent. Manufactured or structured ultra-short-channel-lengthsubstrates are commercially available in a variety of materials capableof withstanding the operating temperature of the partial oxidationreactor.

The mesh substrate disposed within the partial oxidation reactorsupports a catalyst capable of facilitating partial oxidation reactions,wherein a mixture of the hydrocarbon fuel and the first supply ofoxidant are converted to partially-oxidized products, specifically, asynthesis gas comprising hydrogen and carbon monoxide. A suitablepartial oxidation catalyst comprises at least one metal of Group VIII ofthe Periodic Table of the Elements, including iron, cobalt, nickel,ruthenium, rhodium, palladium, osmium, iridium, platinum, and mixturesthereof. The deposition of the Group VIII metal(s) onto the mesh isimplemented by methods well known in the art. Alternatively, finishedcatalysts comprising Group VIII metal(s) supported on the MICROLITHbrand mesh substrate are available from Precision Combustion, Inc.,North Haven, Conn.

In the partial oxidation process, in one embodiment, the mesh substratesupporting the partial oxidation catalyst is initially heated using acommercial ignition device, for example a resistive glow plug heatingelement, disposed within the partial oxidation reactor in closeproximity to the mesh. The hydrocarbon fuel fed to the partial oxidationreactor is likewise heated via the ignition device. The ignition deviceis energized until temperature sensors located within the partialoxidation reactor indicate a temperature sufficient to initiatecatalytic activity (“light-off temperature”). Once the catalyst isignited, the ignition device is de-energized, and energy from theresulting exothermic partial oxidation reaction sustains catalyticoperation without a need for inputting external heat. The ignitiondevice allows for start-up from cold or ambient fuel conditions withouta need for a fuel vaporizer or other external source of heat.

The premixer plenum of the deep oxidation reactor comprises anopen-spaced area designed to mix the partial oxidation product(s) andthe incoming secondary supply of oxidant. Typically, the premixer plenumdoes not contain a foam matrix or any catalyst. In order to retardflashback into the partial oxidation reactor or a diffusion flame fromforming in the premixer plenum, in one embodiment a flamer arrestor isdisposed within the premixer plenum.

The porous matrix of the deep oxidation reactor comprises an open-celledfoam, sponge or other porous material, which is constructed of astructure of struts defining a plurality of open-celled pores andchannels. In one embodiment, the porous matrix possesses a regular andperiodic array of cells, for example, of one size and regulardisposition. In another embodiment, the porous matrix possesses anirregular or asymmetric distribution of different-sized cells windingthrough the strut structure in serpentine fashion. Typically, the porousmatrix has a pore density ranging from about 10 to about 30 pores perinch (10-30 ppi). The porous matrix is provided in any suitable materialof construction sufficiently durable to withstand the operatingtemperature of the deep oxidation reactor. Depending upon temperature, ametallic, ceramic, or cermet porous matrix is suitable, providingacceptable durability at an operating temperature greater than about900° C. Metals are suitable for operating temperatures less than about1,100° C. Suitable non-limiting examples of such metals include theiron-chromium alloys, including FeCrAlY iron-chromium alloy;nickel-chromium alloys and nickel-chromium-iron alloys mentionedhereinabove. Ceramics are preferred for higher operating temperatures,as dictated by the operating temperature of the photovoltaic cell. Inthis instance, ceramics provide durability at a temperature greater thanabout 1,000° C., and more preferably greater than about 1,100° C.Suitable ceramics are selected from various non-metal refractories,non-limiting examples of which include silica, alumina,aluminosilicates, such as calcium aluminosilicates, as well as mullite,silicon carbide, and zirconia.

The photovoltaic cell employed in this invention comprises a photonemitter and at least one photovoltaic diode. The emitter comprises anymaterial capable of radiating photons upon thermal excitation,preferably, with acceptable levels of efficiency and temperatureresistance. Typical emitters operate well between about 900° C. andabout 1300° C., while some can withstand temperatures up to 1,700° C.Emission increases with temperature and is usually at the near-infraredand infrared spectral range. Suitable emitters include, withoutlimitation, polycrystalline silicon carbide, tungsten, rare-earth oxidesincluding ytterbium oxide (Yb₂O₃) and erbium oxide (Er₂O₃), as well asany of present day photonic crystals. The photon emitter is disposeddownstream of the heat spreader, in close proximity thereto, so as tomaximize heat transfer from the heat spreader to the emitter andminimize heat losses to the environment. In one embodiment, the photonemitter is in direct solid-to-solid contact with the heat spreader. Inanother embodiment, a gap exists between the heat spreader and thephoton emitter. The gap is sized to provide for acceptably efficientheat transfer from the heat spreader to the photon emitter. Typically,the photon emitter is disposed at a distance greater than about 3 mm(0.125 inch) and less than about 7.5 cm (3 inches) from the heatspreader.

The photovoltaic diode cell or plurality of such cells is selected fromany of those semi-conductors capable of converting radiant energydirectly into electrical energy. For efficient conversion, absorptioncharacteristics of the diode cell are matched with the emissiveproperties of the photon emitter. Such materials include, withoutlimitation, silicon (Si), germanium (Ge), gallium antimonide (GaSb),germanium antimonide (GeSb), indium gallium arsenide (InGaAs), indiumgallium arsenide antimonide (InGaAsSb), and indium phosphide arsenideantimonide (InPAsSb). The diode is disposed downstream of the photonemitter in a manner that maximizes as much as possible the collection ofall emitted photons. Photons that escape collection can be redirected byuse of mirrors and/or filters back towards the emitter or the diode(s)to improve the efficiency of electrical conversion.

The thermophotovoltaic generator of this invention can be assembled inany manner that allows for efficient and essentially uniformdistribution of heat, photon radiation, and photon collection by thephotoelectric diode cell(s). In one embodiment, as seen in FIGS. 1-3 ,adjacent one face of a disk-shaped photon emitter is disposed a heatspreader of similar shape and diameter; while adjacent an opposite faceof the disk-shaped photon emitter is disposed a circular array ofphotoelectric diodes of overall similar dimensions. In anotherembodiment, as seen in FIG. 4 , a cylindrical-shaped heat spreaderfunctioning as a flame tube is surrounded by an annular-shaped photonemitter; and in return the photon emitter is surrounded by a largerannular-shaped TPV array of photoelectric diode cells. The skilledperson will be able to envision other geometric arrangements of the heatspreader, the photon emitter, and the photoelectric diode cells.

The hydrocarbon fuel fed to the reformer stage is selected from anygaseous or liquid hydrocarbon fuel that is capable of being convertedinto a syngas mixture comprising hydrogen and carbon monoxide. Suitablegaseous hydrocarbon fuels include, without limitation, methane, naturalgas, ethane, ethylene, propane, propylene, butane, pentane, acetylene,fuel gas, bio fuel gas, and mixtures thereof; methane and natural gasbeing preferred. Suitable liquid hydrocarbon fuels include, withoutlimitation, gasoline, kerosene, diesel, jet propulsion fuels, such asJet A and Jet X, biomass fuels, and synthetic fuels obtained fromFisher-Tropsch processes.

The first supply of oxidant fed to the partial oxidation reactorcomprises any chemical capable of partially oxidizing the hydrocarbonfuel selectively to a gaseous partial oxidation product comprisinghydrogen and carbon monoxide (syngas). Suitable oxidants include,without limitation, essentially pure molecular oxygen, mixtures ofoxygen and nitrogen, such as air, and mixtures of oxygen with one ormore inert gases, such as helium and argon.

The hydrocarbon fuel and first supply of oxidant are provided to thepartial oxidation reactor in a “fuel-rich” ratio such that there isinsufficient amount of oxidant present to convert all of the fuel tocomplete oxidation products of carbon dioxide and water. The quantitiesemployed of first supply of oxidant and hydrocarbon fuel are bestdescribed in terms of an O:C ratio, wherein “0” refers to atoms ofoxygen in the first supply of oxidant and “C” refers to atoms of carbonin the hydrocarbon fuel, these being supplied to the partial oxidationreactor. Generally, the O:C ratio of first supply of oxidant tohydrocarbon fuel fed to the partial oxidation reactor is greater thanabout 0.5:1 and less than about 1.2:1.

The POX process desirably involves contacting the hydrocarbon fuel andthe first supply of oxidant in the absence of co-fed external water,steam or mixture thereof. In this instance, the words “co-fed externalwater, steam or mixture thereof” refer to co-feeding, with the suppliesof hydrocarbon fuel and first supply of oxidant, a supply of water,steam, or such mixture thereof as is imported from an external source,for example, an on-board water tank or steam generator or vaporizer.While this application broadly does not prohibit co-feeding water and/orsteam to the reforming process, and while partial oxidation productyields are often enhanced by the addition of co-fed water and/or steam,in the present application co-feeding external water and/or steam mightadd an unnecessary burden.

The POX process operates at a temperature greater than about 700° C. andless than about 1,100° C. and a pressure ranging from sub-ambient toabout 1 psig (6.9 kPa). A suitable gas hourly space velocity measured at21° C. and 1 atm (101 kPa) ranges from about 10,000 liters of combinedsupply of hydrocarbon fuel and first supply of oxidant per liter ofcatalyst bed volume per hour (10,000 hr⁻¹) to about 750,000 hr⁻¹ whichallows for high throughput. A POX efficiency of greater than about 75percent and, preferably, greater than about 80 percent relative toequilibrium is achievable. The partial oxidation reactor is capable ofoperating for greater than about 1,000 hours without indications of cokeproduction and catalyst deactivation.

The partial oxidation product exiting the partial oxidation reactor ispassed into the premixer plenum where the product is supplemented withthe second supply of oxidant fed through the second oxidant inlet. Thesecond supply of oxidant supplied to the premixer plenum comprises anychemical capable of fully combusting the partial oxidation product tocomplete combustion products of carbon dioxide and water, such chemicalsto include air and essentially pure oxygen. In one exemplary embodiment,the first and second supplies of oxidants are identical, and preferably,comprise air. If desired, however, the first supply of oxidant suppliedto the partial oxidation reactor may be different from the second supplyof oxidant supplied to the premixer plenum. The partial oxidationproduct and second supply of oxidant are provided in quantitiessufficient to combust the partial oxidation product (hydrogen, carbonmonoxide, and any unconverted hydrocarbon fuel) completely to carbondioxide and water. Such quantities refer to a “fuel-lean” conditionwherein the quantity of second supply of oxidant exceeds astoichiometric ratio that balances the combustion reaction. Generally,the air-to-fuel mass ratio for this fuel-lean combustion ranges fromabout 10:1 to about 20:1, with combustion efficiencies increasing withincreasing air-to-fuel ratios. Above about 20:1, blow-out may become aproblem.

Temperatures of the gaseous combustion products exiting the deepoxidation reactor range from about 800° C. to about 1,200° C. In oneembodiment, combustion gas exhaust is passed through a recuperatorstructure (FIG. 3 ) to further cool the combustion gases and heat theincoming second supply of oxidant. Combustion gases exiting into theenvironment via the recuperator ideally have at a temperature betweenabout 120° C. and about 250° C. It should be appreciated that thepartial oxidation reaction product comprises hydrogen, which facilitatesa more uniformly distributed combustion across the heat spreader of thedeep oxidation reactor.

EMBODIMENT Example 1

A full scale two-stage combustor with associated photon emitter wasdesigned and tested in accordance with this invention. The combustor wasconstructed as illustrated in FIGS. 1 and 2 , including: a Stage 1catalytic partial oxidation reactor 1 comprised of a fuel inlet 2 forinputting natural gas, an oxidant inlet 3 for inputting air, a catalyticpartial oxidation reaction zone 11 comprising a MICROLITH brandultra-short-channel-length metal substrate 12 having a rhodium catalyst14 supported thereon (Precision Combustion, Inc., North Haven, Conn.), aglow plug 4 for initiating the partial oxidation process, and an outlet5 for exhausting a partial oxidation reaction product comprising carbonmonoxide and hydrogen. Disposed downstream thereof, a Stage 2 deepoxidation combustor comprised a premixer plenum 7 fluidly connected tothe outlet 5 of the partial oxidation reactor 1, the premixer plenum 7further having an inlet 6 for feeding a flow of a secondary oxidant.Downstream of the premixer plenum 7 was positioned an alumina ceramicfoam matrix heat spreader 8 [Ask Chemicals Hi-Tech, L.L.C., AlfredStation, N.Y.; diameter, 3.93 inch (8.26 cm); thickness, 0.375 inch(9.53 mm); 45 pores per inch], wherein deep combustion occurred. Aphoton emitter 9 consisting of a circular quartz plate [McMaster CarrSupply Company, diameter, 4.00 inch (10.16 cm); thickness, 0.05 inch(1.25 mm)] was positioned 0.25 inch downstream of the ceramic foammatrix 8. Combustion gases exhausted to the environment from the gap 16between the ceramic foam matrix 8 and the photon emitter 9.

The apparatus 100 was tested with up to 3.4 kWth natural gas input asfuel via fuel inlet 2 to the catalytic partial oxidation reactor 1. Airwas employed to both the primary oxidant inlet 3 of the partialoxidation reactor 1 and the secondary oxidant inlet 6 to the premixerplenum 7. The catalytic partial oxidation reaction zone 11 was operatedat a fuel-rich O:C ratio sufficient to maintain a temperature of 950° C.in the POX reactor to produce a product mixture of hydrogen (H₂) andcarbon monoxide (CO). The deep combustion stage 8 was operated at atemperature of 1,100° C. under fuel-lean conditions, that is, withexcess air so as to provide for complete conversion of the partialoxidation reaction products to carbon dioxide (CO₂) and water (H₂O).Combustion occurred within the ceramic foam matrix 8 under diffusionflame conditions. A thermocouple was placed at a center position on theupstream face of the quartz plate contacting the gaseous combustionproduct.

FIG. 5 depicts a graph of temperature versus time during operation ofthe two-stage combustor. The temperature at the center of the quartzplate was held at 1,100° C. during the test. The heat produced in thetwo-stage combustor was efficiently transferred to the quartz platephoton emitter, which appeared to have a uniform infrared glow. It isreliably expected that the emitted photons initiate a photoelectricreaction in an associated TPV diode cell for production of electricity.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions, or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

The invention claimed is:
 1. A thermophotovoltaic generator comprising:(1) a two-stage combustor; (2) a photon emitter disposed in thermalcommunication with the two-stage combustor; and (3) at least onephotovoltaic diode cell disposed in radiative communication with thephoton emitter; wherein the two-stage combustor comprises: (a) a partialoxidation reactor comprising the following components: (i) a fuel inlet,(ii) a first oxidant inlet, (iii) a partial oxidation reaction zonecomprising a mesh substrate having a partial oxidation catalystsupported thereon, the partial oxidation reaction zone being disposed influid communication with the fuel inlet and the first oxidant inlet, and(iv) an outlet fluidly connected to the partial oxidation reaction zone;and (b) a deep oxidation reactor comprising the following components:(i) a premixer plenum having an upstream end and a downstream end;wherein at the upstream end the premixer plenum is fluidly connected tothe outlet of the partial oxidation reactor; and further wherein thepremixer plenum comprises a second oxidant inlet; (ii) a heat spreaderhaving an upstream end and a downstream end; wherein at the upstream endthe heat spreader is fluidly connected to the downstream end of thepremixer plenum; and further wherein the heat spreader comprises aporous matrix capable of withstanding a temperature greater than about900° C.; and (iii) an outlet pathway fluidly connected to the downstreamend of the heat spreader.
 2. The thermophotovoltaic generator of claim 1wherein the mesh substrate comprises an ultra-short-channel-length meshsubstrate having a channel length in a range from 50 microns to 500microns.
 3. The thermophotovoltaic generator of claim 1 wherein theporous matrix comprises a porous ceramic foam matrix capable ofoperating at a temperature greater than 1,000° C.
 4. Thethermophotovoltaic generator of claim 3 wherein the porous ceramic foammatrix is selected from the group consisting of silica, alumina,aluminosilicates, zirconia, silicon carbide, and mullite.
 5. Thethermophotovoltaic generator of claim 3 wherein the porous ceramic foammatrix has from 20 to 40 pores per inch.
 6. The thermophotovoltaicgenerator of claim 3 wherein the porous ceramic foam matrix does notcomprise a catalyst.
 7. The thermophotovoltaic generator of claim 1wherein the photon emitter is selected from the group consisting ofquartz, polycrystalline silicon carbide, tungsten, rare-earth oxidesincluding ytterbium oxide and erbium oxide and photonic crystals.
 8. Thethermophotovoltaic generator of claim 1 wherein the diode cell iscomprised of a semi-conductor selected from the group consisting ofgermanium, germanium antimonide, indium gallium arsenide, indium galliumarsenide antimonide, and indium phosphide arsenide antimonide.
 9. Aprocess of producing electricity in the thermophotovoltaic generator ofclaim 1, comprising: (a) feeding a hydrocarbon fuel and a first supplyof oxidant into the catalytic partial oxidation reactor; (b) contactingthe resulting mixture of hydrocarbon fuel and the first supply ofoxidant in the presence of the partial oxidation catalyst supported onthe mesh substrate under fuel-rich process conditions sufficient toproduce a partial oxidation reaction product comprising hydrogen andcarbon monoxide; (c) passing the partial oxidation reaction product intothe premixer plenum and mixing said product with a second supply ofoxidant; (d) combusting the resulting mixture of the partial oxidationreaction product and the second supply of oxidant within the porousmatrix heat spreader at a temperature greater than 900° C. and underfuel lean conditions so as to produce a gaseous combustion productcomprising carbon dioxide and water; (e) transferring heat from thegaseous combustion product to the photon emitter with resulting emissionof photons; and (f) collecting the photons in a diode photovoltaic cellwherein a photoelectric reaction occurs to produce electricity.
 10. Theprocess of claim 9 wherein the combustion occurs in the heat spreadernon-catalytically.
 11. The process of claim 9 wherein the mesh substratecomprises an ultra-short-channel-length mesh substrate having a channellength ranging from 50 microns to 500 microns.
 12. The process of claim9 wherein the heat spreader comprises a ceramic foam matrix selectedfrom the group consisting of silica, alumina, aluminosilicates,zirconia, silicon carbide, and mullite, and wherein optionally, theceramic foam matrix has from 20 to 40 pores per inch.
 13. The process ofclaim 9 wherein the photon emitter is selected from the group consistingof quartz, polycrystalline silicon carbide, tungsten, rare-earth oxidesincluding ytterbium oxide and erbium oxide and photonic crystals. 14.The process of claim 9 wherein the diode cell is comprised of asemi-conductor selected from the group consisting of germanium,germanium antimonide, indium gallium arsenide, indium gallium arsenideantimonide, and indium phosphide arsenide antimonide.